This invention relates to a process for preparing short chain alkyl phenols by alkylating an aromatic compound with a relatively short chain alkylating agent employing a synthetic porous crystalline material, or zeolite, as alkylation catalyst.
Zeolitic materials, both natural and synthetic, have been demonstrated in the past to have catalytic properties for various types of hydrocarbon conversion. Certain zeolitic materials are ordered, porous crystalline aluminosilicates having a definite crystalline structure as determined by X-ray diffraction within which there are a large number of smaller cavities which may be interconnected by a number of still smaller channels or pores. These cavities and pores are uniform in size within a specific zeolitic material. Since the dimensions of these pores are such as to accept for adsorption molecules of certain dimensions while rejecting those of larger dimensions, these materials have come to be known as "molecular sieves" and are utilized in a variety of ways to take advantage of these properties. Such molecular sieves, both natural and synthetic, include a wide variety of positive ion-containing crystalline silicates. These silicates can be described as a rigid three-dimensional framework of SiO.sub.4 and Periodic Table Group IIIA dimensional framework of SiO.sub.4 and Periodic Table Group IIIA element oxide, e.g., AlO.sub.4, in which the tetrahedra are cross-linked by the sharing of oxygen atoms whereby the ratio of the total Group IIIA element, e.g., aluminum, and silicon atoms to oxygen atoms is 1.2. The electrovalence of the tetrahedra containing the Group IIIA element, e.g., aluminum, is balanced by the inclusion in the crystal of a cation, e.g., an alkali metal the ratio of the Group IIIA element, e.g., aluminum, to the number of various cations, such as Ca, Sr, Na, K or Li, is equal to unity. One type of cation may be exchanged either entirely or partially with another type of cation utilizing ion exchange techniques in a conventional manner. By means of such cation exchange, it has been possible to vary the properties of a given silicate by suitable selection of the cation. The spaces between the tetrahedra are occupied by molecules of water prior to dehydration.
Prior art techniques have resulted in the formation of a great variety of synthetic zeolites. Many of these zeolites have come to be designated by letter or other convenient symbols, as illustrated by zeolite Z (U.S. Pat. No. 2,882,243), zeolite X (U.S. Pat. No. 2,882,244), zeolite Y (U.S. Pat. No. 3,130,007), zeolite ZK-5 (U.S. Pat. No. 3,247,195), zeolite ZK-4 (U.S. Pat. No. 3,314,752), zeolite ZSM-5 (U.S. Pat. No. 3,702,886), zeolite ZSM-11 (U.S. Pat. No. 3,709,979), zeolite ZSM-12 (U.S. Pat. No. 3,832,449), zeolite ZSM-20 (U.S. Pat. No. 3,972,983), zeolite ZSM-35 (U.S. Pat. No. 4,016,245), and zeolite ZSM-23 (U.S. Pat. No. 4,076,842), merely to name a few.
The SiO.sub.2 /Al.sub.2 O.sub.3 ratio of a given zeolite is often variable. For example, zeolite X can be synthesized with SiO.sub.2 /Al.sub.2 O.sub.3 ratios of from 2 to 3; zeolite Y, from 3 to about 6. In some zeolites, the upper limit of the SiO.sub.2 /Al.sub.2 O.sub.3 ratio is unbounded. ZSM-5 is one such example wherein the SiO.sub.2 /Al.sub.2 O.sub.3 ratio is at least 5 and up to the limits of present analytical measurement techniques. U.S. Pat. No. 3,941,871 (Re. 29,948) discloses a porous crystalline silicate made from a reaction mixture containing no deliberately added alumina in the recipe and exhibiting the X-ray diffraction pattern characteristic of ZSM-5. U.S. Patent Nos. 4,061,724, 4,073,85 and 4,104,294 describe crystalline silicates of varying alumina and metal content.
Short chain alkylphenols are commercially important end products and process intermediates. As end products they are used as antioxidants, stabilizers, and additives, for example, as radical trapping agents in plastics, elastomers, synthetic fibers, fuels, lubricants, and foods. As intermediates they are used, for example, in oxidation reactions to produce hydroquinones.
Production of these compounds by conventional methods, for example, by the alkylation of phenol in the presence of conventional alkylation catalysts, is, however, somewhat problematic in that the reaction yields a broad spectrum of products. Isolation or enrichment of specific positional isomers is both difficult and expensive.
Traditionally, alkylation reactions are generally carried out at atmospheric pressure with the reactants in the liquid phase utilizing catalysts such as sulfuric acid, boron trifluoride, aluminum chloride or strongly acidic ion exchange resins. Some zeolites, specifically REX and HY, have been reported in the scientific literature as catalyzing the reaction of a relatively long chain alkylating agent, i.e. 1-decyl alcohol, with phenol at atmospheric pressure and 200.degree. C. the product of that reaction was predominantly an ortho/para mixture of decylphenols with side chain attachment largely at the second and third carbon atoms of the alkyl group.
U.S. Pat. No. 4,283,573 describes a process for producing relatively long chain alkylphenols by alkylation of phenol with a long chain alkylating agent possessing one or more available alkyl groups of at least 5 carbon atoms in length employing as catalyst a zeolite such as cancrinite, gmelinite, mordenite, offretite or ZSM-12.
While zeolites, such as ZSM-12, have found utility in producing relatively long chain alkylphenols, it is desirable to have higher selectivity and conversion ratios for the production of short chain alkyl phenols than ZSM-12 can provide.